Printing press with hot air dryer

Abstract

The invention relates to a printing press comprising a hot-air dryer (2) having a nozzle action distance (A) of up to 20 mm between a nozzle face (6) and a transport path (1) of a sheet in an active position for drying the sheet. The hot-air dryer (2) is mounted so as to be movable away from the transport path (1) of the sheet into a passive position. The hot-air dryer (2) is controlled so as to continue to blow hot air in the passive position. The transport path (1) can be formed by a cylinder.

Description

TECHNICAL FIELD

[0001] The invention relates to a printing press comprising a hot-air dryer having a nozzle action spacing of at most 20 mm between a nozzle face and a sheet transport path in an active position for drying a sheet, wherein the hot-air dryer is mounted so as to be movable away from the sheet transport path into a passive position. BACKGROUND

[0002] Such a printing press is described in DE 10 2009 054 865 A1.

[0003] In a printing press having a hot-air dryer there is the risk that machine components arranged around the dryer are excessively loaded with heat.

[0004] In order to overcome this risk it is suggested in DE 10 2007 019 977 A1 to select a favourable mounting position for the dryer.

[0005] In practice, however, the selection of the mounting position is often very limited. SUMMARY

[0006] It is therefore the task of the invention to provide a printing press having a hot-air dryer in which the heat load of critical machine components around is reduced.

[0007] This task is solved by a printing press comprising a hot-air dryer having a nozzle action spacing of at most 20 mm between a nozzle face and a sheet transport path in an active position for drying a sheet, wherein the hot-air dryer is mounted so as to be movable away from the sheet transport path into a passive position, characterized in that the hot-air dryer is controlled so as to continue to blow hot air in the passive position.

[0008] By moving the hot-air dryer into the passive position the distance between the transport path and the nozzle is increased, whereby the heat load of components forming the transport path, for example sheet transport cylinders, is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0009] In other alternative embodiments and from the following description of the figures, extensions are derived which are mentioned in the following:

[0010] Figure 1 A first embodiment is shown in which the dryer is in the active position;

[0011] Figure 2 The dryer of the first embodiment is shown in the passive position;

[0012] Figure 3A second embodiment is shown, in which both dryer segments are in the active position respectively;

[0013] Figure 4 The two dryer segments of the second embodiment are shown, in the passive position respectively. DETAILED DESCRIPTION

[0014] Both embodiments have the following in common:

[0015] The conveying path 1 of the sheet is formed by cylinders, which convey the printed sheet (not shown together) through the hot-air dryer. The printing press, which is provided with the hot-air dryer 2, can be an inkjet printer, but is preferably a lithographic sheet offset printing press.

[0016] The dryer segment 3 or each dryer segment 3, 4 of the hot-air dryer 2 has a plenum 5 and a nozzle face 6. The dryer segment 3, 4 is beam-shaped and extends transversely to the conveying direction T of the sheet.

[0017] A blower, which generates the hot blast air, and an air dryer can be arranged in the plenum 5 or connected to the plenum 5 by a hose in the case of separate, position-fixed arrangement of the blower and the air dryer. In the case of arrangement of the blower and the air dryer on the dryer segment 3, 4, the blower and the air dryer move together when the dryer segment 3, 4 moves.

[0018] The hot blast air from the plenum 5 is blown out through nozzles 7 in the nozzle face 6, not only in the active position (1 or 3) of the respective dryer segment 3, 4, but also in the passive position (2 or 4). Figure 1 Figure 2

[0019] The nozzles 7 are round nozzles with a round nozzle cross-section. They can be configured as bores milled into the nozzle face 6 or as tubes inserted into the nozzle face.

[0020] The hot blast air is shown schematically in Figure 3 and 4 by arrows. The temperature of the blown-out hot blast air is higher than 200°C, in particular higher than 250°C and for example approximately 300°C.

[0021] In the active position of the dryer segment 3, 4, the nozzle action gap A between the nozzle face 6 and the conveying path 1, for example the cylinder circumference on which the sheet lies, is at most 20 mm. The nozzle action gap A is in the range from 2 mm to 20 mm. Thus, the hot-air dryer 2 is a so-called impingement jet dryer, due to the nozzle action gap, which has a magnitude of only a few millimetres. In the passive position of the dryer segment 3, 4, its spacing from the conveying path 1 is greater than 20 mm, for example 200 mm.​​

[0022] The hot-air dryer 2 is mounted so as to be swingable into the active position by means of a joint or hinge 8. Alternatively, the hot-air dryer 2 is mounted so as to be movable into the active position by means of, for example, linear guide means. In both the rotary and the translatory mounting variants, the adjustment movement of the hot-air dryer 2 is driven by at least one and preferably a plurality of adjustment drives in the form of, for example, pneumatic cylinders. The adjustment drives 9 are not shown in Figure 3 and 4 .

[0023] Figure 1 and 2 the first embodiment in

[0024] Figure 3 and 4 the second embodiment has a plurality of features:

[0025] The hot-air dryer 2 here comprises a plurality of dryer sections - a first dryer section 3 and a second dryer section 4. The two dryer sections 3, 4 are moved in opposite directions from the active position into the passive position and back again, for example after a printing job has been interrupted. In moving from one position to the other, the respective dryer section 3, 4 is swung through an angle of approximately 90°.

[0026] In the passive position, the nozzle faces 6 of the two dryer sections 3, 4 face one another. The additional advantage resulting therefrom is that the hot air ejected from the dryer sections 3, 4 in the passive position no longer points towards the conveying path 1. This is also advantageous in that the hot-air dryer 2 no longer continues to eject hot air in the passive position. Here, the thermal radiation output by the nozzle faces 6 no longer points towards the conveying path 1.

[0027] An advantage of all the embodiments is that the hot-air dryer 2 can continue to be operated without interruption even when the printing job is interrupted, i.e. it does not have to be switched off. Thereby, a loss of operating time is avoided, which would otherwise have to be accepted for the purpose of stopping and subsequently starting the dryer. The hot-air dryer 2 only has to be moved away from the conveying path 1 when the printing job is interrupted, for example in the event of an emergency stop or stand-by. With the hot-air dryer 2 remaining in the passive position, it is also possible to pre-heat the hot-air dryer 2 before the printing job is started and to cool it down after the printing job has ended.

[0028] By the present application not only an undesired heating of the critical components (in particular the conveying path 1) around the hot-air dryer 2 is avoided, but also a fire hazard. Without the measures of the present application this fire hazard could exist in the case that the cylinders forming the conveying path 1 and the printed sheets lying thereon are in a rotational position at an emergency stop in which the printed sheets are in the target region of the hot-air dryer 2 which continues to run or which is not cooled down fast enough due to a sluggish reaction.

[0029] List of reference signs

[0030] 1 conveying path

[0031] 2 hot-air dryer

[0032] 3 dryer section

[0033] 4 dryer section

[0034] 5 plenum

[0035] 6 nozzle face

[0036] 7 nozzle

[0037] 8 joint

[0038] 9 adjustment drive

[0039] A nozzle action distance

[0040] T conveying direction

Claims

1. A printing machine comprising a hot-air dryer (2) having a nozzle action distance (A) of up to 20 mm between a nozzle face (6) and a transport path (1) of a sheet in an active position for drying a sheet, wherein the hot-air dryer (2) is mounted so as to be movable away from the transport path (1) of the sheet into a passive position, characterized in that The hot-air dryer (2) is actuated to continue to blow hot air in the passive position.

2. The printing press according to claim 1, characterized in that The hot-air dryer (2) has a first dryer section (3) and a second dryer section (4).

3. The printing press according to claim 2, characterized in that In the passive position, the nozzle faces (6) of the first dryer section (3) and the second dryer section (4) face each other.

4. The printing press according to any one of claims 1 to 3, characterized in that The conveying path (1) is formed by a drum.

5. The printing press according to any one of claims 1 to 3, characterized in that The hot-air dryer (2) has nozzles (7) configured as round nozzles.

6. The printing press according to any one of claims 1 to 3, characterized in that The hot-air dryer (2) is actuated to have a blow-off stream temperature of more than 200°C.

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